Reactive Sintering Process of Ferromagnetic MnBi under High Magnetic Fields J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-17 Yoshifuru Mitsui, Rie Y. Umetsu, Kohki Takahashi, Keiichi Koyama
The magnetic field effect on the reactive sintering process of MnBi was investigated. Magnetic-field-induced enhancement of the reaction was found to be exhibited at the initial stages. The coercivity field decreased with an increase in the in-field annealing time. Additionally, as the in-field annealing time was increased, the anisotropy field improved by 65% to 3.5 T. The kinetics of the reaction were in good agreement with the diffusion-controlled reaction model. It is suggested that the decrease in activation energy at the initial stages of reaction increased the amount of formed MnBi phases, resulting in enhancement of the reaction Mn + Bi to MnBi phase by in-field reactive sintering.
The magnetic properties of BaCo0.5Ni0.5F4 J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-17 Qingyu Xu, Chuanjun Dai, Zhida Han, Qi Li
The family of BaMF4 with M of magnetic 3d transition metal ions is the typical multiferroic material. Pure phase solid solution of BaCoF4 and BaNiF4 with molar ratio of 1:1 (BaCo0.5Ni0.5F4) is prepared by solid state reaction, which has been confirmed by X ray diffraction patterns. Field dependent magnetization measurements only show the linear curve with temperature down to 5 K, indicating the antiferromagnetic nature. Compared with BaCoF4 and BaNiF4, no significant enhancement of magnetization is observed, indicating the absence of ferrimagnetism and the random distribution of Co and Ni ions. The low temperature magnetic anomalies are studied by zero field cooled (ZFC) and field cooled (FC) temperature dependent magnetization (M-T) measurements. A bifurcation between FC and ZFC M-T curves happens at 118 K, indicating the onset of 2-dimensional antiferromagnetism. The magnetization maximum at 87 K is attributed to the 2-dimensional antiferromagnetic clusters, followed by the drastic decrease of magnetization, which is due to the onset of 3-dimensional antiferromagnetism. A dip is observed in FC M-T curve at 40 K, which is attributed to the 3-dimensional antiferromagnetic clusters. A drastic increase of magnetization is observed at 9 K, which is due to the uncompensated isolated spins. Exchange bias is clearly observed, with blocking temperature of 90 K. The contribution from surface spin glass has been excluded by the AC magnetization measurements, and the mechanism has been explained by the exchange coupling between the two antiferromagnetic phases.
High Microwave Attenuation Performance of Planar Carbonyl Iron Particles with Orientation of Shape Anisotropy Field J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-17 Cheng Guo, Zhihong Yang, Shile Shen, Juan Liang, Guoyue Xu
Planar anisotropy carbonyl iron (PACI) particles were prepared from commercial spherical carbonyl iron particles through a high performance ball-milling technique. The paraffin composites with orientation of shape anisotropy field for these PACI particles were obtained by applying an external magnetic field during the fabrication process. The frequency-dependent complex permeability values of these prepared paraffin composites have been investigated in the frequency range of 1-18 GHz. The results demonstrate that the orientation of shape anisotropy field for these PACI particles can effectively increase the complex permeability and decrease the complex permittivity values. Benefit from the enhancement in the complex permeability and reduction in the complex permittivity, the better impedance matching condition can be obtained and thus the good microwave absorption performance can be achieved for the samples with enough magnetic field orientation time.
Effects of sintering temperature on properties of toroid cores using NiZnCu ferrites for power applications at >1 MHz J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-16 Junchang Liu, Yunhui Mei, Wen Liu, Xin Li, Feng Hou, Guo-Quan Lu
A mechanical characterisation on multiple timescales of electroconductive magnetorheological elastomers J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-16 M. Schümann, J. Morich, T. Kaufhold, V. Böhm, K. Zimmermann, S. Odenbach
Magnetorheological elastomers are a type of smart hybrid material which combines elastic properties of a soft elastomer matrix with magnetic properties of magnetic micro particles. This leads to a material with magnetically controllable mechanical properties of which the magnetorheological effect is the best known. The addition of electroconductive particles to the polymer mix adds electrical properties to the material behaviour. The resulting electrical resistance of the sample can be manipulated by external magnetic fields and mechanical loads. This results in a distinct interplay of mechanical, electrical and magnetic effects with a highly complex time behaviour. In this paper a mechanical characterisation on multiple time scales was conducted to get an insight on the short and long-term electrical and mechanical behaviour of this novel material. The results show a complex resistivity behaviour on several timescales, sensitive to magnetic fields and strain velocity. The observed material exhibits fatigue and relaxation behaviour, whereas the magnetorheological effect appears not to interfere with the piezoresistive properties.
Plateau on Temperature Dependence of Magnetization of Nanostructured Rare Earth Titanates J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-16 A.B. Rinkevich, A.V. Korolev, M.I. Samoylovich, S.O. Demokritov, D.V. Perov
Magnetic properties of nanocomposite materials containing particles of rare earth titanates of R2Ti2O7 type, where R is a rare earth ion, including “spin ice” materials are investigated. The descending branches of hysteresis loop have been studied in detail in temperature range from 2 to 50 K. It has been shown that nanocomposites with Yb2Ti2O7, Dy2Ti2O7 and Er2Ti2O7 particles have one intersection point of the descending branches in some temperature range unlike many other nanocomposites. It is shown that magnetization has only weak temperature dependence near this point. It has been obtained that nanocomposites with Pr2Ti2O7 and Nd2Ti2O7 particles have no hysteresis loop. All above findings point out to unusual magnetic structures of the studied samples.
Feasibility study evaluating a magnetic marker in an ex-vivo porcine model J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-16 Mirjam C.L. Peek, Ali Zada, Muneer Ahmed, Rose Baker, Masaki Sekino, Moriaki Kusakabe, Michael Douek
Magnetization reversal of thin ferromagnetic elements with surface anisotropy J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-12 N.A. Usov, O.N. Serebryakova
The magnetization reversal process in thin-film ferromagnetic elements with surface anisotropy of various shapes and sizes is investigated by means of numerical simulation. The dependencies of the perpendicular and in-plane hysteresis loops on the element thickness, and the value of the surface anisotropy constant are obtained. For sufficiently large values of the surface anisotropy constant the magnetization reversal of thin-film elements is shown to occur due to the nucleation of the buckling mode. For an elongated rectangular element the nucleation field of the buckling mode is proportional to the absolute value of the surface anisotropy constant, and inversely proportional to the element thickness. Prime Novelty Statement It is shown that analyzing the magnetization reversal process in thin-film ferromagnetic elements with surface anisotropy one can determine the actual value of the surface magnetic anisotropy by means of comparison of experimental and numerical simulation data. The properties of thin ferromagnetic films with surface anisotropy are promising for applications of such magnetic materials in modern thin-film electronics devices.
Variation of Microwave Magnetic Properties for Thin Films of Ferromagnetic Metals with the Film Thickness J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-12 Stanislav Y. Bobrovskii, Igor T. Iakubov, Andrei N. Lagarkov, Sergei A. Maklakov, Sergei S. Maklakov, Aleksei V. Osipov, Konstantin N. Rozanov, Ilya A. Ryzhikov, Dmitrii A. Petrov, Polina A. Zezyulina
An investigation of the dependence of magnetic properties on the thickness of ferromagnetic films was completed. The study dealt with magnetostatic and microwave measurements of single-layer films of ferromagnetic metals (Fe, Co) and was aimed at revealing reasons for the deterioration of microwave magnetic performance with an increase in film thickness. Two types of variation of microwave permeability with the film thickness were distinguished for the films under study. One exhibited a noticeable deviation from maximal values and was observed for Co. The other case involved a gradual worsening of performance, and was observed for Fe. In the first case, the resonance frequency shifted lower when the film was thicker than 0.2-0.4 μm, and Acher’s coefficient fell by the factor of three. In the second case, the microwave performance worsened gradually, and a decrease of Acher’s coefficient was not large, approximately by 20%. The data analysis showed that the reason for the deterioration is an increase of out-of-plane anisotropy in the first case and sufficient growth of damping factor in the second case.
Large Resistance Change on Magnetic Tunnel Junction based Molecular Spintronics Devices J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-12 Pawan Tyagi, Edward Friebe
Molecular bridges covalently bonded to two ferromagnetic electrodes can transform ferromagnetic materials and produce intriguing spin transport characteristics. This paper discusses the impact of molecule induced strong coupling on the spin transport. To study molecular coupling effect the octametallic molecular cluster (OMC) was bridged between two ferromagnetic electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the exposed side edges. OMCs induced strong inter-ferromagnetic electrode coupling to yield drastic changes in transport properties of the magnetic tunnel junction testbed at the room temperature. These OMCs also transformed the magnetic properties of magnetic tunnel junctions. SQUID and ferromagnetic resonance studies provided insightful data to explain transport studies on the magnetic tunnel junction based molecular spintronics devices.
Magnetic Field-Mediated Two Magnetic States in BiFeO3/CoPt Layered Structures J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-12 Yue Wang, Takashi Harumoto, Jian Wang, Eiji Suzuki, Katsuyuki Nakada, Yoshio Nakamura, Shigeki Nakagawa, Ji Shi
BiFeO3/L1°CoPt layered films are prepared by sputtering on MgO (001) substrates. Both X-ray diffraction and transmission electron microscopy confirm the (001)-epitaxial growth. Magnetic field-mediated two magnetic states phenomenon has been observed in this layered films. Element mapping results indicate there exist Co-deficient CoPt layer (∼ 1.5 nm) and Co-containing BiFeO3 layer (∼ 2 nm) adjacent to the BiFeO3/CoPt interface. After applying in-plane or out-of-plane external magnetic field, moments in the above layers react differently, leading to two disparate magnetic states: coupling and decoupling states.
Determination of magnetic domain state of carbon coated iron nanoparticles via 57Fe zero-external-field NMR J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-11 M. Manjunatha, Rajeev Kumar, Balaram Sahoo, Ramakrishna Damle, K.P. Ramesh
The magnetic domain state of carbon coated iron nanopowder (Fe@C) was studied by the internal field nuclear magnetic resonance (IFNMR) at 77 K using the spin echo technique. The structure and magnetic properties of the sample were further characterized by scanning electron microscopy (SEM), X-Ray diffraction (XRD), Mössbauer spectroscopy, vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA) and Raman Spectroscopy. The obtained IFNMR results of Fe@C powder were compared with that of micron sized carbonyl iron (CI) and electrolytic iron (EI) powders. The calculated critical size of the single domain state of iron particles in Fe@C is ∼ 16 nm. A higher enhancement in echo amplitude was observed due to the better response of the domain walls of multidomain particles in comparison to the single domain particles. The echo signal of CI and EI particles exhibit a single narrow intense peak corresponding to the domain walls, whereas Fe@C exhibits two low amplitude peaks at two different frequencies: a low frequency (46.6 MHz) peak corresponds to the response of the domain walls of the multidomain particles and the other high frequency (47.2 MHz) signal (a shoulder) corresponding to the response of the magnetic nuclei inside the domain. Our results help in determining the domain state of iron-based magnetic particles using 57Fe-IFNMR.
Heterojunction-induced magnetic anisotropy and magnetization reversal of Ni wires on LiNbO3 substrate J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-11 Akinobu Yamaguchi, Takuo Ohkochi, Akira Yasui, Toyohiko Kinoshita, Keisuke Yamada
Through-Process Characterization of Local Anisotropy of Non-oriented Electrical Steel Using Magnetic Barkhausen Noise J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-11 Youliang He, Mehdi Mehdi, Erik J. Hilinski, Afsaneh Edrisy
Magnetic Barkhausen noise (MBN) signals were measured on a non-oriented electrical steel through all the thermomechanical processing stages, i.e. hot rolling, hot band annealing, cold rolling and final annealing. The temperature of the final annealing was varied from 600°C to 750°C so that the steel consisted of partially or completely recrystallized microstructures and different levels of residual stresses. The angular MBNrms (root mean square) values were compared to the texture factors in the same directions, the latter being calculated from the crystallographic texture measured by electron backscatter diffraction (EBSD). It was found that, in the cold-rolled, hot-rolled and completely recrystallized steels, the angular MBNrms followed a cosine function with respect to the angle of magnetization, while in partially recrystallized state such a relation does not exist. After cold rolling, the maximum MBNrms was observed in the rolling direction (RD) and the minimum MBNrms was in the transverse direction (TD), which was inconsistent with the magnetocrystalline anisotropy as indicated by the texture factor. After hot rolling, the maximum and minimum MBNrms values were observed in the TD and RD, respectively, exactly opposite to the cold-rolled state. If the steel was completely recrystallized, the maximum MBNrms was normally observed at a direction that was 15°-30° from the minimum texture factor. If the steel was partially recrystallized, both the magnetocrystalline anisotropy of the material and the residual stress contributed to the angular MBNrms, which resulted in the deviation of the relationship from a cosine function. The relative strength of the two factors determined which factor would dominate the overall magnetic anisotropy.
Monocrystalline Heusler Co2FeSi alloy glass-coated microwires: fabrication and magneto-structural characterization J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-11 L. Galdun, T. Ryba, V.M. Prida, V. Zhukova, A. Zhukov, P. Diko, V. Kavečanský, Z. Vargova, R. Varga
Large scale production of single crystalline phase of Heusler Co2FeSi alloy microwire is reported. The long microwire (∼ 1 km) with the metallic nucleus diameter of about 2 µm is characterized by well oriented monocrystalline structure (B2 phase, with the lattice parameter a = 5.615 Å). Moreover, the crystallographic direction  is parallel to the wirés axis along the entire length. Additionally, the wire is characterized by exhibiting a high Curie temperature (Tc > 800 K) and well-defined magnetic anisotropy mainly governed by shape. Electrical resistivity measurement reveals the exponential suppression of the electron-magnon scattering which provides strong evidence on the half-metallic behaviour of this material in the low temperature range.
Improved Equivalent Magnetic Network Modeling for Analyzing Working Points of PMs in Interior Permanent Magnet Machine J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-09 Liyan Guo, Changliang Xia, Huimin Wang, Zhiqiang Wang, Tingna Shi
As is well known, the armature current will be ahead of the back electromotive force (back-EMF) under load condition of the interior permanent magnet (PM) machine. This kind of advanced armature current will produce a demagnetizing field, which may make irreversible demagnetization appeared in PMs easily. To estimate the working points of PMs more accurately and take demagnetization under consideration in the early design stage of a machine, an improved equivalent magnetic network model is established in this paper. Each PM under each magnetic pole is segmented, and the networks in the rotor pole shoe are refined, which makes a more precise model of the flux path in the rotor pole shoe possible. The working point of each PM under each magnetic pole can be calculated accurately by the established improved equivalent magnetic network model. Meanwhile, the calculated results are compared with those calculated by FEM. And the effects of d-axis component and q-axis component of armature current, air-gap length and flux barrier size on working points of PMs are analyzed by the improved equivalent magnetic network model.
Electronic and magnetic properties of magnetoelectric compound Ca2CoSi2O7: an ab initio study J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-09 Jayita Chakraborty
The detailed first principle density functional theory calculations are carried out to investigate the electronic and magnetic properties of magnetoelectric compound Ca2CoSi2O7. The magnetic properties of this system are analyzed by calculating various hopping integrals as well as exchange interactions and deriving the relevant spin Hamiltonian. The dominant exchange path is visualized with Wannier functions plotting. Only intra planer nearest neighbor exchange interaction is strong in this system. The magnetocrystalline anisotropy is calculated for this system, and the results of the calculation reveal that the spin quantization axis lies in the ab plane.
Study of electrical and magnetic properties of RE doped layered cobaltite thin films J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-09 K. Bapna, R.J. Choudhary, D.M. Phase, R. Rawat, B.L. Ahuja
Thin films of layered perovskites Sr1.5RE0.5CoO4 (RE=La, Gd) were grown on MgO (001) substrate using pulsed laser ablation method. Structural, electrical and magnetic properties of single phase oriented films were studied. Films reveal semiconducting behavior in the entire measured temperature range. The films show thermally activated behavior at high temperature regime, with a higher value of activation energy for SGCO than that for SLCO. The low temperature behavior is well fitted with 3D-variable range hopping mechanism. Both films showed negative magneto-resistance measured in temperature range of 10-200K. The value of MR is large for SGCO film as compared to its bulk counterpart as well as SLCO film, suggesting its high potential in the spintronics applications. A pinch-shaped M-H behaviour as observed in both the films, suggests the presence of two-magnetic phases. Occurrence of pinch-shape behaviour is although in line with that of SLCO bulk counterpart, interestingly, it was absent in SGCO polycrystalline powder. It suggests major role of film growth kinetics in modifying the magnetic properties in cobaltites.
Magnetodielectric effect in (1-x)(Ba0.88Ca0.12)(Ti0.88Zr0.12)O3 − xCoFe2O4 J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-09 Pengfei Pan, Jin Tao, Fusheng Ma, Ning Zhang
Magnetodielectric (MD) materials have attracted considerable attention due to their intriguing physics and potential future applications. In this work, polycrystalline (1-x)(Ba0.88Ca0.12)(Ti0.88Zr0.12)O3 − xCoFe2O4 (x = 0.10, 0.20, 0.30, 0.40) ceramic have been prepared via sol−gel method. The room temperature magnetic and ferroelectric behaviors of the synthesized composites were investigated. For the composite with x = 0.40, a MD ratio of 5.37% was achieved under a magnetic field of 1.5 T at f = 1 kHz. The measured “butterfly hysteresis” MD curves exhibit an obvious dielectric anomaly. Theoretical analysis suggests that the observed magnetodielectric effect is attributed to the magnetoresistance effect and magnetoelectric coupling.
Structural, optical, dielectric and magnetic studies of Gadolinium-added Mn-Cu nanoferrites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-09 R. Rajesh Kanna, N. Lenin, K. Sakthipandi, A. Senthil Kumar
Spinel ferrite with the general formula Mn1-xCuxFe1.85Gd0.15O4 (x= 0.2, 0.4, 0.6 and 0.8) was synthesized using the standard sonochemical method. The structure, optical, morphology, dielectric and magnetic properties of the prepared Mn1-xCuxFe1.85Gd0.15O4 nanoferrites were exhaustively investigated using various characterization techniques. The phase purity, secondary phase and crystallite parameters were studied from X-ray diffraction patterns. Fourier transform infrared spectra showed two absorption bands of transition metal oxides in the frequency range from 400 to 650 cm-1, which are related to asymmetric stretching modes of the spinel ferrites (AB2O4). Raman spectra have five active modes illustrating the vibration of O2- ions at both tetrahedral (A) site and octahedral (B) site ions. The wide and narrow scan spectrum from X-ray photoelectron spectroscopy results confirmed the presence of Mn, Cu, Gd, Fe, C and O elements in the composition. The oxidation state and core level of the photo electron peaks of Mn 2p, Cu 2p, Gd 3d, Fe 2p and O 1s were analyzed. The influence of the Cu2+ concentration in Mn1-xCuxFe1.85Gd0.15O4 on the morphology, varying from nanorods, nanoflakes to spherical, was explored on the basis of scanning electron microscopy images. Ultraviolet diffuse reflectance spectroscopy studies indicated that the optical bandgap (5.12-5.32 eV) of the nanoferrites showed an insulating behavior. The dielectric constant, loss tangent and complex dielectric constant values decreased with an increase in frequency with the addition of Gd3+ content. A vibrating sample magnetometer showed that the prepared nanoferrites had a soft ferromagnetic nature. The magnetic parameter changed markedly with an increase in the Cu content in Mn1-xCuxFe1.85Gd0.15O4 nanoferrites. The optical, dielectric and magnetic properties were considerably enhanced with the addition of Gd3+ ions in the spinel nanoferrites.
Heusler Alloys with bcc Tungsten Seed Layers for GMR Junctions J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-08 William Frost, Atsufumi Hirohata
We demonstrate that polycrystalline Co2FeSi Heusler alloys films can be grown with perpendicular anisotropy without the use of an MgO interface. By heating the substrate to 400°C prior to deposition and using a tungsten seed layer perpendicular anisotropy is induced in the Heusler layer. This is maintained as the thickness of the Co2FeSi is increased up to 12.5nm. The layers with thickness dependent coercivity can be implemented into a giant magnetoresistance structure leading to spin-valve behaviour without the need for an exchange biased pinned layer.
“Metamagnetoelectric” effect in multiferroics J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-08 G.C. Fouokeng, F. Kuate Fodouop, M. Tchoffo, L.C. Fai, N. Randrianantoandro
We present a theoretical calculation of magnetoelectric properties in a quasi-two dimensional spin chain externally controlled by a static electric field in y-direction and magnetic field in z-direction. Given the diversity of properties in functional materials and their applications in physics, the multiferroic model is investigated. By using the Fermi-Dirac statistics of quantum gases and the Landau theory, we assess the effects of the Dzyaloshinskii-Moriya interaction and the electric polarization on the magnetoelectric coupling that induces at low temperature the “metamagnetoelectric” effet, and likewise affects the ferroelectricity induced through symmetry mechanisms and magnetic properties of the multiferroic system. In fact, the variation of the induced polarisation due to spin arrangement through the Dzyaloshinskii-Moriya interaction gives rise to a multistep interdependant metamagnetic and metaelectric transitions which are settled up by the corresponding Dzyaloshinskii-Moriya parameter and the system then exhibits a spin gap that results from an electric and a magnetic demagnetization field range. This metamagnetoelectric effect observed in these multiferoic materials model is seem to be highly tunable via the external electric and magnetic fields and thus can be crucial in the design of new mechanisms for the processing and storage of data and other spintronic applications.
The anisotropic tunneling behavior of spin transport in graphene-based magnetic tunneling junction J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-08 Mengchun Pan, Peisen Li, Weicheng Qiu, Jianqiang Zhao, Junping Peng, Jiafei Hu, Jinghua Hu, Wugang Tian, Yueguo Hu, Dixiang Chen, Xuezhong Wu, Zhongjie Xu, Xuefeng Yuan
Due to the theoretical prediction of large tunneling magnetoresistance (TMR), graphene-based magnetic tunneling junction (MTJ) has become an important branch of high-performance spintronics device. In this paper, the non-collinear spin filtering and transport properties of MTJ with the Ni/tri-layer graphene/Ni structure were studied in detail by utilizing the non-equilibrium Green’s formalism combined with spin polarized density functional theory. The band structure of Ni-C bonding interface shows that Ni-C atomic hybridization facilitates the electronic structure consistency of graphene and nickel, which results in a perfect spin filtering effect for tri-layer graphene-based MTJ. Furthermore, our theoretical results show that the value of tunneling resistance changes with the relative magnetization angle of two ferromagnetic layers, displaying the anisotropic tunneling behavior of graphene-based MTJ. This originates from the resonant conduction states which are strongly adjusted by the relative magnetization angles. In addition, the perfect spin filtering effect is demonstrated by fitting the anisotropic conductance with the Julliere’s model. Our work may serve as guidance for researches and applications of graphene-based spintronics device.
Lattice dynamics, elasticity and magnetic abnormality in ordered crystalline alloys Fe3Pt at high pressures J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-06 Tai-min Cheng, Guo-Liang Yu, Yong Su, Chong-Yuan Ge, Xin-Xin Zhang, Zhu Lin, Li Lin
The ordered crystalline Invar alloy Fe3Pt is in a special magnetic critical state, under which the lattice dynamic stability of the system is extremely sensitive to external pressures. We studied the pressure dependence of enthalpy and magnetism of Fe3Pt in different crystalline alloys by using the first-principles projector augmented-wave method based on the density functional theory. Results show that the P4/mbm structure is the ground state structure and is more stable relative to other structures at pressures below 18.54 GPa. The total magnetic moments of L12, I4/mmm and DO22 structures decrease rapidly with pressure and oscillate near the ferromagnetic collapse critical pressure. At the pressure of 43 GPa, the ferrimagnetic property in DO22 structure becomes apparently strengthened and its volume increases rapidly. The lattice dynamics calculation for L12 structures at high pressures shows that the spontaneous magnetization of the system in ferromagnetic states induces the softening of the transverse acoustic phonon TA1 (M), and there exists a strong spontaneous volume magnetostriction at pressures below 26.95 GPa. Especially, The lattice dynamics stability is sensitive to pressure, in the pressure range between the ferromagnetic collapse critical pressure (41.9 GPa) and the magnetism completely disappearing pressure (57.25 GPa), and near the pressure of phase transition from L12 to P4/mbm structure (27.27 GPa). Moreover, the instability of magnetic structure leads to a prominent elastic modulus oscillation, and the spin polarizability of electrons near the Fermi level is very sensitive to pressures in that the pressure range. The pressure induces the stability of the phonon spectra of the system at pressures above 57.25 GPa.
Design of lightweight broadband microwave absorbers in the X-band based on (polyaniline/MnNiZn ferrite) nanocomposites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-06 Nassim Nasser Ali, Rama Al-Qassar Bani Al-Marjeh, Yomen Atassi, Akil Salloum, Adnan Malki, Mojtaba Jafarian
We present the design of novel, lightweight, broadband microwave absorbers based on polyaniline/Mn0.1Ni0.45Zn0.45Fe2O4 (PANI/MnNiZn ferrite) nanocomposites. The ferrite is synthesized by sol-gel technique. Then, the polymer is deposited by in-situ chemical oxidative polymerization. The structural and morphological characterizations of the composites are investigated by SEM, XRD, FT-IR and UV-vis spectroscopy. The functional characterization is performed by measuring the dc-conductivity and microwave absorption characteristics in the X-band. The absorbers exhibit broad bandwidths under -10dB ranging from 2.60 to 3.74GHz and low surface density ranging from 2.5-3.1 kg/m2. The absorber of 3.74GHz bandwidth has a minimum reflection loss of -31.32dB at 11.13 GHz with a matching thickness of 3mm and a low loading in paraffin of only 25% w/w.
Particle-size distribution modified effective medium theory and validation by magneto-dielectric Co-Ti substituted BaM ferrite composites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-05 Qifan Li, Yajie Chen, Vincent G. Harris
This letter reports an extended effective medium theory (EMT) including particle-size distribution functions to maximize the magnetic properties of magneto-dielectric composites. It is experimentally verified by Co-Ti substituted barium ferrite (BaCoxTixFe12-2xO19)/wax composites with specifically designed particle-size distributions. In the form of an integral equation, the extended EMT formula essentially takes the size-dependent parameters of magnetic particle fillers into account. It predicts the effective permeability of magneto-dielectric composites with various particle-size distributions, indicating an optimal distribution for a population of magnetic particles. The improvement of the optimized effective permeability is significant concerning magnetic particles whose properties are strongly size dependent.
Study of microstructure and magnetotransport properties of CrO2 prepared under HTHP J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-05 Y.B. Fan, R.K. Zheng, G.H. Wen
The microstructure of the CrO2 particles prepared by high temperature and high pressure (HTHP) method was studied by HRTEM. It is found that the CrO2 particles synthesized at 500 and 550 °C are covered by Cr2O3 surface layers of about 6 nm thick. However, the CrO2 particles synthesized at 400 and 450 °C do not have Cr2O3 surface layers. The saturation magnetization of the CrO2 particles synthesized at different temperatures is all very close to the theoretical value. The magnetoresistance (MR) of the CrO2 particles synthesized at 500 and 550 °C is much larger than that of the CrO2 particles synthesized at 400 and 450 °C, which should be due to the enhancement of tunneling magnetoresistance by insulating Cr2O3 surface layers. The tunneling MR of the CrO2 particles can be fitted well by expression of C1(M/Ms)2+C2(M/Ms)4+C3(M/Ms)6. The proportion of the higher-order terms of (M/Ms)2 in the expression is tightly related to the existence of the Cr2O3 surface layer.
Quantum information generation, storage and transmission based on nuclear spins J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-04 V.V. Zaharov, V.I. Makarov
A new approach to quantum information generation, storage and transmission is proposed. It is shown that quantum information generation and storage using an ensemble of N electron spins encounter unresolvable implementation problems (at least at the present time). As an alternative implementation we discuss two promising radical systems, one with N equivalent nuclear spins and another with N nonequivalent nuclear spins. Detailed analysis shows that only the radical system containing N nonequivalent nuclei is perfectly matched for quantum information generation, storage and transmission. We develop a procedure based on pulsed electron paramagnetic resonance (EPR) and we apply it to the radical system with the set of nonequivalent nuclei. The resulting EPR spectrum contains 2N 2 N transition lines, where N is the number of the atoms with the nuclear spin 1 2 , and each of these lines may be encoded with a determined qudit sequence. For encoding the EPR lines we propose to submit the radical system to two magnetic pulses in the direction perpendicular to the z axis of the reference frame. As a result, the radical system impulse response may be measured, stored and transmitted through the communications channel. Confirming our development, the ab initio analysis of the system with three anion radicals was done showing matching between the simulations and the theoretical predictions. The developed method may be easily adapted for quantum information generation, storage, processing and transmission in quantum computing and quantum communications applications.
Effect of Al-doped YCrO3 on structural, electronic and magnetic properties. J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-04 A. Durán, E. Verdín, A. Conde, R. Escamilla
Structural, dielectric and magnetic properties were investigated in the YCr1-xAlxO3 with 0 < x < 0.5 composition. XRD and XPS studies show that the partial substitution of the Al3+ ion decreases the cell volume of the orthorhombic structure without changes in the oxidation state of the Cr3+ ions. We discuss two mechanisms that could have a significant influence on the magnetic properties. The first is related to local deformation occurring for x < 0.1 of Al content and the second is related to change of the electronic structure. The local deformation is controlled by the inclination of the octahedrons and the octahedral distortion having a strong effect on the TN and the coercive field at low Al concentrations. On the other hand, the decreasing of the magnetization values (Mr and Hc) is ascribed to changes in the electronic structure, which is confirmed by a decreasing of the contribution of Cr 3d states at Fermi level due to increasing Al3+ content. Thus, we analyzed and discussed that both mechanisms influence the electronic properties of the YCr1-xAlxO3 solid solution.
Structural, Electronic, Magnetic, Elastic, and Thermal properties of Co-based Equiatomic Quaternary Heusler alloys J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-04 Ramesh Paudel, Jingchuan Zhu
In this research work, we have predicted the physical properties of CoFeZrGe and CoFeZrSb for the first time by utilizing first principle calculations based on density functional theory. The exchange-correlation potentials are treated within the generalized-gradient approximation of Perdew-Burke and Ernzerhof(GGA-PBE). The investigated equilibrium lattice parameters of CoFeCrSi are in agreement with available theoretical data and for CoFeZrZ(Z=Ge,Sb) are 6.0013 and 6.2546Å respectively. The calculated magnetic moments are 1.01μB μ B /fu, 2μB μ B /fu and 1μB μ B /fu for CoFeZrZ(Z= Ge, Sb and Si)respectively, and agree with the Slater-Pauling rule, Mt=Zt-24 M t = Z t - 24 . The CoFeZrGe, CoFeZrSb and CoFeZrSi composites showed half-metallic behaviour with 100% 100 % spin polarization at equilibrium lattice parameters with band gap of 0.43, 0.70 and 0.59 eV for GGA and an improved band gap of 0.86, 1.01 and 1.08 for GGA+U respectively. Elastic properties are also discussed in this paper and it is found that all the materials are mechanically stable and ductile in nature. The CoFeZrSi alloy is found to be stiffer than CoFeZrZ(Z= Ge and Sb) alloys. The Debye temperatures are predicted by using calculated elastic constants. Moreover, the volume heat capacities (Cv) ( C v ) are investigated by utilizing the quasi-harmonic Debye model.
The influence of bias magnetization of nanoparticles on GMR sensor signal and sensitivity for the ultra-low concentration detection J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-04 Yang Zhang, Jie Xu, Derang Cao, Qiang Li, Guoxia Zhao, Nian X. Sun, Shandong Li
In the broad research of the GMR bio-sensing technology, it is vital to explore appropriate magnetic labels and its influences on the detection signal. In this work, four kinds of ferrite particles of γ-Fe2O3, CoFe2O4, NiFe2O4 and NiZnFe2O4 were prepared through calcining the Dimethyl Formamide (DMF) solution of the transition metal nitrates [Fe(NO3)3 and X(NO3)2, X=Co, Ni, Zn] to study the effect of magnetic properties on detection signals using a DC in-plane measuring method. It was revealed that for four particles, the output voltage differences |ΔV| between with and without magnetic particles exhibit log-linear functions of the particles concentrations x in the range from 0.1 to 10 ng/mL. A very low limitation of detection (LOD) of 0.1 ng/mL for all the samples was obtained, which is two orders smaller than that in the previous work. Moreover, the change of output voltage difference at the LOD (|ΔVlim|) is proportional to the magnetization at bias field (bias magnetization, Mbias), which indicates that larger Mbias leads to a lower LOD. This work provides a useful guidance in selecting or preparing magnetic labels to enhance the sensitivity of GMR biosensors.
Large magnetoresistance dips and perfect spin-valley filter induced by topological phase transitions in silicene J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-04 Worasak Prarokijjak, Bumned Soodchomshom
Spin-valley transport and magnetoresistance are investigated in silicene-based N/TB/N/TB/N junction where N and TB are normal silicene and topological barriers. The topological phase transitions in TB's are controlled by electric, exchange fields and circularly polarized light. As a result, we find that by applying electric and exchange fields, four groups of spin-valley currents are perfectly filtered, directly induced by topological phase transitions. Control of currents, carried by single, double and triple channels of spin-valley electrons in silicene junction, may be achievable by adjusting magnitudes of electric, exchange fields and circularly polarized light. We may identify that the key factor behind the spin-valley current filtered at the transition points may be due to zero and non-zero Chern numbers. Electrons that are allowed to transport at the transition points must obey zero-Chern number which is equivalent to zero mass and zero-Berry's curvature, while electrons with non-zero Chern number are perfectly suppressed. Very large magnetoresistance dips are found directly induced by topological phase transition points. Our study also discusses the effect of spin-valley dependent Hall conductivity at the transition points on ballistic transport and reveals the potential of silicene as a topological material for spin-valleytronics.
Temperature dependent and applied field strength dependent magnetic study of Cobalt Nickel ferrite nano particles: Synthesized by an environmentally benign method J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-03 S.Uday Bhasker, G. Narsinga Rao, F.C. Chou, M.V. Ramana Reddy
Spinel ferrites have come a long way in their versatile applications. The ever growing applications of these materials demand detailed study of material properties and environmental considerations in their synthesis. In this article, we report the effect of temperature and applied magnetic field strength on the magnetic behavior of the cobalt nickel ferrite nano powder samples. Basic structural properties of spinel ferrite nano particles, that are synthesized by an environmentally benign method of auto combustion, are characterized through XRD, TEM, RAMAN spectroscopy. Diffuse Reflectance Spectroscopy (DRS) is done to understand the nickel substitution effect on the optical properties of cobalt ferrite nano particles. Thermo magnetic studies using SQUID in the temperature range 5K to 400K and room temperature (300K) VSM studies are performed on these samples. Fields of 0Oe (no applied field: ZF), 1kOe (for ZFC and FC curves), 5kOe (0.5T), 50kOe (5T) (for M-H loop study) are used to study the magnetic behavior of these nano particles. The XRD,TEM analysis suggest 40nm crystallites that show changes in the cation distribution and phase changes in the spinel structure with nickel substitution. Raman micrographs support phase purity changes and cation redistributions with nickel substitution. Diffuse reflectance study on powder samples suggests two band gap values for nickel rich compounds. The Magnetic study of these sample nano particles show varied magnetic properties from that of hard magnetic, positive multi axial anisotropy and single-magnetic-domain structures at 5K temperature to soft magnetic core shell like structures at 300K temperature. Nickel substitution effect is non monotonous. Blocking temperature of all the samples is found to be higher than the values suggested in the literature.
Possibility of a Ferromagnetic and Conducting Metal-Organic Network J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-03 Manel Mabrouk, Roland Hayn, Hassan Denawi, Rafik Ben Chaabane
In this paper, we present first principles calculations based on the spin-polarized generalized gradient approximation with on-site Coulomb repulsion term (SGGA+U), to explore the electronic and magnetic properties of the novel planar metal-organic networks TM-Pc and TM-TCNB (where TM means a transition metal of the 3d series: Ti, V, Cr, ..., or Zn, Pc - Phthalocyanine, and TCNB - Tetracyanobenzene) as free-standing sheets. This work is an extension of two earlier research works dealing with the Mn (M. Mabrouk et al., Phys. Rev. B: Condens. Matter Mater. Phys. 92 (2015) 184424) and Fe (M. Mabrouk et al., J. Phys. Chem. C 121 (2017) 4253) cases. Our theoretical investigations demonstrate that TM-Pc are more stable than TM-TCNB. Our results unveil that all the TM-Pc frameworks have an insulating behavior with the exception of Mn-Pc which is half-metallic and favor antiferromagnetic order in the case of our magnetic systems except for V-Pc which is ferromagnetic. In contrast, the TM-TCNB networks are metallic at least in one spin direction and exhibit long-range ferromagnetic coupling in case for magnetic structures, which represent ideal candidates and an interesting prospect of unprecedented applications in spintronics. In addition, these results may shed light to achieve a new pathway on further experimental research in molecular spintronics.
Microstructure and characterization of W-type hexaferrite Ba1-xLaxFe22+Fe163+O27 prepared by solid state method J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-02 Jin Tang, Xiansong Liu, Khalid Mehmood Ur Rehman, Dan Li, Mingling Li, Yujie Yang
We report a successful preparation of Ba1-xLaxFe22+Fe163+O27 (x=0.00-0.10) W-type hexagonal ferrites by standard ceramic method in a reduced oxygen atmosphere. In this work, the effect of the substitution La3+ rare-earth ions for Ba2+ ions on the structural and magnetic properties of the prepared samples have been studied. The phase identification of magnetic powders was performed by X-ray diffraction. The results of XRD show that the single phase was observed in the W-type ferrites with different La content. The SEM micrographs showed that the ferrites have formed the hexagonal structure. The magnetic properties of the samples were metric by a vibrating sample magnetometer. The coercivity (Hc) of the particles decreases with the increase of La content(x), while the saturation magnetization (Ms) of the particles first increases with x from 0 to 0.05, and then begins to decrease when x continues to increase. The monotonic dependence of the magnetic anisotropy field Ha and coercivity Hc on the La3+ doping amount is found to be mainly dominated by the competition between Ms and Keff.
A comparative study of the physical properties of Cu-Zn ferrites annealed under different atmospheres and temperatures: Magnetic enhancement of Cu0.5Zn0.5Fe2O4 nanoparticles by a reducing atmosphere J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-02 Ahmad Gholizadeh
In the present work, the influence of different sintering atmospheres and temperatures on physical properties of the Cu0.5Zn0.5Fe2O4 nanoparticles including the redistribution of Zn2+ and Fe3+ ions, the oxidation of Fe atoms in the lattice, crystallite sizes, IR bands, saturation magnetization and magnetic core sizes have been investigated. The fitting of XRD patterns by using Fullprof program and also FT-IR measurement show the formation of a cubic structure with no presence of impurity phase for all the samples. The unit cell parameter of the samples sintered at the air- and inert-ambient atmospheres trend to decrease with sintering temperature, but for the samples sintered under carbon monoxide-ambient atmosphere increase. The magnetization curves versus the applied magnetic field, indicate different behaviour for the samples sintered at 700°C with the respect to the samples sintered at 300°C. Also, the saturation magnetization increases with the sintering temperature and reach a maximum 61.68 emu/g in the sample sintered under reducing atmosphere at 600 °C. The magnetic particle size distributions of samples have been calculated by fitting the M–H curves with the size distributed Langevin function. The results obtained from the XRD and FTIR measurements suggest that the magnetic core size has the dominant effect in variation of the saturation magnetization of the samples.
Effects of Co2O3 on electromagnetic properties of NiCuZn ferrites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-02 Shuoqing Yan, Sheng Liu, Jun He, Heng Luo, Longhui He, Yuhan Li, Shengxiang Huang, Lianwen Deng
The effects of Co2O3 addition on the electromagnetic properties of NiCuZn ferrite were investigated, by considering the variation of complex permeability, complex permittivity and quasi-microwave absorption property in the 1∼1000 MHz frequency range. Results show that the introduction of Co3+ ions in NiCuZn ferrite leads to the marked shifting of magnetic resonance towards high-frequency and a slight increase of the permittivity. These Co-related effects enhance the maximum reflection loss in NiCuZn ferrite to reach -55.1 dB with its absorption bandwidth being tunable in the frequency range 480 to 1000 MHz, which provides a potential absorber for the anti-electromagnetic interference applications in electronic industry.
Synthesis, characterization and microwave characteristics of ATP/BaFe12O19/PANI ternary composites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-02 Dezhong Bai, Huixia Feng, Nali Chen, Lin Tan, Jianhui Qiu
In this paper, we introduced attapulgite (ATP) into the system of ferrite composites for the first time. By sol-gel self-propagating combustion method, attapulgite/barium ferrite (ATP/BaFe12O19) was prepared, and then ternary composites of attapulgite/barium ferrite/polyaniline (ATP/BaFe12O19/PANI) were obtained by in-situ oxidative polymerization of aniline on ATP/BaFe12O19 mixture. The phase composition, morphology and electromagnetic properties of the as-prepared composites were characterized by X-ray diffraction (XRD), Transmission election microscope (TEM), Fourier transform infrared (FTIR), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). We found that the ATP/BaFe12O19/PANI composites at a thickness of 2 mm have the minimum reflection loss of −11.89 dB at 11.28 GHz, besides the effective absorption bandwidth (less than −5 dB) reached 6.39 GHz (from 8.42 GHz to 14.81 GHz).
Enhanced magneto-optical and photo-catalytic properties of transition metal cobalt (Co2+ ions) doped spinel MgFe2O4 ferrite nanocomposites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-02 A. Godlyn Abraham, A. Manikandan, E. Manikandan, S. Vadivel, S.K. Jaganathan, A. Baykal, P. Sri Renganathan
In this study, spinel magnesium cobalt ferrite (CoxMg1-xFe2O4: x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) nanocomposites were synthesized successfully by modified sol-gel combustion method. Magnesium nitrate, cobalt nitrate and iron nitrate were used as the source of divalent (Mg2+ and Co2+) and trivalent (Fe3+) cations, respectively and urea were used as the reducing (fuel) agent. The effects of cobalt ions on morphology, structural, optical, magnetic and photo-catalytic properties of spinel CoxMg1-xFe2O4 nanocomposites were investigated. Various characterization methods, including X-ray powder diffraction (XRD), high resolution scanning electron microscope (HR-SEM), transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transforms infrared (FT-IR) spectroscopy, vibrating sample magnetometer (VSM) and photo-catalytic degradation (PCD) activity were used to study the phase purity, microstructure, particle size, elemental composition, functional group determination, band gap calculation, magnetic properties and degradation efficiency of nanoparticles, respectively. The observed results showed that the final products consists cubic spinel phase with sphere-like nanoparticles morphologies. Furthermore, spinel Co0.6Mg0.4Fe2O4 nanocomposites showed highest PCD efficiency (98.55%) than other composition of ferrite nanoparticles.
Hydrogen Absorption and its Effect on Magnetic Properties of Nd2Fe14B J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-01-02 R. Bezdushnyi, R. Damianova, I.S. Tereshina, N.Yu. Pankratov, S.A. Nikitin
Magnetic properties of hydrides of the intermetallic compound Nd2Fe14BHxNd2Fe14BHx are investigated in the temperature range covering the Curie temperatures (TCTC) of the compounds (up to 670 K). The temperature dependencies of magnetization are measured under continuous control of hydrogen content in the investigated samples. The dependencies of Curie and spin-reorientation transition (TSRTSR) temperatures on the hydrogen concentration are studied in detail. The dependence of hydrogen concentration on pressure at a constant temperature (near TCTC) and on the temperature at various pressures are obtained. We attempted to estimate the contributions of the unit cell volume increase upon hydrogenation and the electronic structure change in the variation of TCTC of the hydrogenated Nd2Fe14BNd2Fe14B.
Two dimensional compass model with Heisenberg interactions J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-30 A.S.T. Pires
We consider a two dimensional compass model with a next and a next near Heisenberg term. The interactions are of two types: frustrated near neighbor compass interactions of amplitudes Jx and Jy, and next and next near neighbor Heisenberg interactions with exchanges J1 and J2 respectively. The Heisenberg interactions are isotropic in spin space, but the compass interactions depend on the bond direction. The ground state of the pure compass model is degenerated with a complex phase diagram. This degeneracy is removed by the Heisenberg terms leading to the arising of a magnetically ordered phase with a preferred direction. We calculate the phase diagrams at zero temperature for the case where, for J2 = 0, we have an antiferromagnetic ground state. We show that varying the value of J2, a magnetically disordered phase can be reached for small values of the compass interactions. We also calculate the critical temperature for a specified value of parameters.
Phase transitions of the frustrated bilayer spin one XY model J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-30 A.S.T. Pires
In this paper we use the SU(3) Schwinger boson representation, followed by a mean field decoupling, to study the disordered phases of the bilayer spin one quantum XY antiferromagnet on a square lattice with next near neighbor and a single ion anisotropy. The phase diagram at zero temperature is obtained. The ratio η=J⊥/J1 η = J ⊥ / J 1 between the interlayer J⊥ J ⊥ to the intralayer near neighbor J1 exchange interactions exhibits a quantum phase transition at a critical ratio ηc=21.725 η c = 21.725 that separates the small- η Nèel phase from the large η quantum disordered paramagnet. The effect of next near neighbor interactions is discussed. The Neel phase is studied using a self consistent harmonic approximation that takes into account topological effects.
The influence of goethite nanorods on structural transitions in liquid crystal 6CHBT J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-30 Peter Kopčanský, Veronika Gdovinová, Segii Burylov, Natalia Burylova, Alexey Voroshilov, Jozefína Majorošová, Filippo Agresti, Valentina Zin, Simona Barison, Jan Jadźyn, Natália Tomašovičová
This work is devoted to the study of composite system of liquid crystal 4-(trans-4-n-hexylcyclohexyl)-isothiocyanato-benzene (6CHBT) doped with lathlike goethite magnetic nanoparticles with the concentration of 0.01 vol%. The structural transitions in ferronematic samples were observed by dielectric measurements in a capacitor made of ITO-coated glass electrodes as well as by polarizing optical microscopy. Due to the presence of magnetic particles a decrease of the magnetic Fréedericksz transition was observed. The response of ferronematics to very low magnetic fields is also presented which opens the door towards application possibilities such as low magnetic fields sensors.
Structural, optical and magnetic properties of Co doped ZnO DMS nanoparticles by microwave irradiation method J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-30 D. Guruvammal, S. Selvaraj, S. Meenakshi Sundar
New grafted ferrite particles/liquid crystal composite under magnetic field J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-29 D. Manaila Maximean
A new colloidal composite formed by specially synthesized dimethylphenyl ferrite particles and a nematic liquid crystal (LC) is presented. By applying a small magnetic field during polarizing optical microscopy observations, it was found that the magnetic moment of the synthesized ferrite is perpendicular to the director of the LC. The optical transmission of laser light across the ferronematic was investigated under magnetic field. The critical magnetic field corresponding to the Freedericksz transition was obtained and discussed according to the Burylov and Raikher theory.
Structural, multiferroic, dielectric and magnetoelectric properties of (1-x)Ba0.85Ca0.15Ti0.90Zr0.10O3-(x)CoFe2O4 lead-free composites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-28 N.S. Negi, Rakesh Kumar, Hakikat Sharma, J. Shah, R.K. Kotnala
High performance lead-free multiferroic composites with strong magnetoelectric coupling effect are desired to replace lead-based ceramics in multifunctional device applications due to increasing environmental issues. We report crystal structure, ferroelectric, magnetic, dielectric and magnetoelectric properties of (1-x)Ba0.85Ca0.15Ti0.90Zr0.10O3-(x)CoFe2O4 (BCTZ-CFO) lead-free composites with x = 0.1, 0.3, 0.5, 0.7 and 0.9 synthesized by chemical solution method. BCTZ power was synthesized by sol-gel method while CFO was prepared by metallo-organic decomposition (MOD) method. The XRD results confirm successful formation of the BCTZ-CFO composites without presence of any impurity phase. At room temperature, the BCTZ-CFO composites show multiferroic behavior characterized by ferroelectric and ferromagnetic hysteresis curves. The composite having 10 wt.% of CFO exhibited maximum polarization, remnant polarization and coercive field of Ps ∼ 5.1 µC/cm2, Pr ∼ 1.4 µC/cm2 and Ec ∼ 11.6 kV/cm respectively. The BCTZ-CFO composite with 90 wt.% of CFO incorporation exhibits improved ferromagnetic properties with Ms ∼ 32 emu/g, Mr ∼ 11.7 emu/g and Hc ∼ 504 Oe. Mӧssbauer spectra analysis show two sets of six-line hyperfine patterns for BCTZ-CFO composites, indicating the presence of Fe3+ ions in both A and B sites. Increasing BCTZ content was found to decrease the hyperfine field strength at both sites and is consistent with the decreasing magnetic moment observed for the samples. The maximum dielectric constant value ε′ ∼ 678 is obtained at 1 MHz for composite with 10 wt.% of CFO phase. The results indicate that the BCTZ-CFO composites are potential lead-free room temperature multiferroic systems.
Crossover phenomena in the critical range near magnetic ordering transition J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 U. Köbler
Among the most important issues of Renormalization Group (RG) theory are crossover events and relevant (or non-relevant) interactions. These terms are unknown to atomistic theories but they will be decisive for future field theories of magnetism. In this experimental study the importance of these terms for the critical dynamics above and below magnetic ordering transition is demonstrated on account of new analyses of published data. When crossover events are overlooked and critical data are fitted by a single power function of temperature over a temperature range including a crossover event, imprecise critical exponents result. The rather unsystematic and floating critical exponents reported in literature seem largely to be due to this problem. It is shown that for appropriate data analyses critical exponents are obtained that are to a good approximation rational numbers. In fact, rational critical exponents can be expected when spin dynamics is controlled by the bosons of the continuous magnetic medium (Goldstone bosons). The bosons are essentially magnetic dipole radiation generated by the precessing spins. As a result of the here performed data analyses, critical exponents for the magnetic order parameter of β=1/2, 1/3, 1/4 and 1/6 are obtained. For the critical paramagnetic susceptibility the exponents are γ=1 and γ=4/3.
Magnetic resonance studies of mixed chalcospinel CuCr2SxSe4-x (x=0; 2) and CoxCu1-xCr2S4 (x=0.1; 0.2) nanocrystals with strong interparticle interactions J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 A.I. Pankrats, A.M. Vorotynov, V.I. Tugarinov, S.M. Zharkov, G.M. Zeer, K. Ramasamy, A. Gupta
Magnetic resonance characteristics of mixed chalcospinel nanocrystals CuCr2SxSe4-x (x = 0 and 2) and CoxCu1−xCr2S4 (x = 0.1 and 0.2) have been investigated. It has been established based on TEM, SEM and resonance data that all the samples contain both blocks with sizes from 1 to 50 m of compacted nanosized crystallites and individual nanoparticles with sizes from 10 to 30 nm. The studies provide evidence of strong interparticle interaction in all the samples leading to high values of the blocking temperature. Magnetic dipolar field arise in the boundary regions of interacting adjacent nanocrystals below the blocking temperature. This results in inhomogeneous broadening of the magnetic resonance spectrum along with appearance of additional absorption lines. With increase in magnetic anisotropy at low temperatures, a shift of the resonance field along with line broadening are observed for all the studied compounds due to freezing of the moments in the nanoparticles, both in the individual and compacted ones. A gapped characteristic of the resonance spectrum is established below the freezing temperature Tfr, with the energy gap defined by the averaged magnetic anisotropy <HA>. Anionic substitution of sulfur by selenium results in a decrease in the magnetic anisotropy. In contrast, cationic substitution of copper by cobalt increases the magnetic anisotropy due to a strong contribution from the latter ion.
Manipulating the magnetic anisotropy and magnetization dynamics by stress: Numerical calculation and experiment J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 M.A. Correa, F. Bohn
We perform a theoretical and experimental investigation of the magnetic properties and magnetization dynamics of a ferromagnetic magnetostrictive multilayer grown onto a flexible substrate and submitted to external stress. We calculate the magnetic behavior and magnetoimpedance effect for a trilayered system from an approach that considers a magnetic permeability model for planar geometry and a magnetic free energy density which takes into account induced uniaxial and magnetoelastic anisotropy contributions. We verify remarkable modifications of the magnetic anisotropy with external stress, as well as we show that the dynamic magnetic response is strongly affected by these changes. We discuss the magnetic features that lead to modifications of the frequency limits where distinct mechanisms are responsible by the magnetoimpedance variations, enabling us to manipulate the resonance fields. To test the robustness of the approach, we directly compare theoretical results with experimental data. Thus, we provide experimental evidence to confirm the validity of the theoretical approach, as well as to manipulate the resonance fields to tune the MI response according to real applications in devices.
Study of dipolar interaction in amorphous microwires using longitudinally driven magneto-impedance effect J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 W.Q. Yu, J.T. Zou, X. Li, H.L. Pan, Q. Zhang, W.H. Xie, Z.J. Zhao
The long-range dipole-dipole interaction in an array of Co57.3Fe7.6Cr1.7C33.4 amorphous microwires with axial bistability has been studied through magnetic hysteresis and longitudinally driven magneto-impedance (LDMI) measurements in this paper. Hysteresis loops performed for an array of microwires exhibit jumps and plateaux on the demagnetization curves. For LDMI curves, the multi-peak characteristic is presented as the number of microwires changes from 1 to 4. Each step in the hysteresis loops or each peak in the LDMI curves is correspondent to the magnetization reversal of an individual wire. To analysis the difference between the switching field of hysteresis loops and the peak field of LDMI curves, we further studied the dependence of the peak field on the driving current. The results showed that the ac magnetic field has a compensatory effect on the magnetization reversal of an individual wire.
Phase Composition And Magnetic Properties In Hot Deformed Magnets Based On Misch-Metal J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 Q. Ma, Z.Y. Zhang, X.F. Zhang, Z.F. Hu, Y.L. Liu, F. Liu, X.M. Jv, J. Wang, Y.F. Li
Thermodynamic model of a solid with RKKY interaction and magnetoelastic coupling J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 T. Balcerzak, K. Szałowski, M. Jaščur
Thermodynamic description of a model system with magnetoelastic coupling is presented. The elastic, vibrational, electron and magnetic energy contributions are taken into account. The long-range RKKY interaction is considered together with the nearest-neighbour direct exchange. The generalized Gibbs potential and the set of equations of state are derived, from which all thermodynamic functions are self-consistently obtained. Thermodynamic properties are calculated numerically for FCC structure in arbitrary external pressure, magnetic field and temperature, and widely discussed. In particular, for some parameters of interaction potential and electron concentration corresponding to antiferromagnetic phase, the existence of negative thermal expansion coefficient is predicted.
Large magnetoresistance in a directionally solidified Ni44.5Co5.1Mn37.1In13.3 magnetic shape memory alloy J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 Zongbin Li, Wei Hu, Fenghua Chen, Mingang Zhang, Zhenzhuang Li, Bo Yang, Xiang Zhao, Liang Zuo
Polycrystalline Ni44.5Co5.1Mn37.1In13.3 alloy with coarse columnar-shaped grains and <0 0 1>A preferred orientation was prepared by directional solidification. Due to the strong magnetostructural coupling, inverse martensitic transformation can be induced by the magnetic field, resulting in large negative magnetoresistance up to -58% under the field of 3T. Such significant field controlled functional behaviors should be attributed to the coarse grains and strong preferred orientation in the directionally solidified alloy.
Effects of Annealing on Microstructure, Composition and Magnetic Properties of Rolled Fe/Ga-Al Composite Strip J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 Yanwen Zheng, Zhihao Zhang, Yanbin Jiang
The Ga liquid and Al powder were mechanically mixed and poured into a hollow iron plate, after alloying, the composite plate was rolled at room temperature for preparing an Fe/Ga-Al composite strip. The effect of annealing conditions on the diffusion, microstructures and magnetostrictive properties of the strip were studied. The composite plate had good cold rolling formability. After annealing at 750∼850 °C for 5 h of the cold-rolled sample with a reduction of 97%, the diffusion distance of Ga and Al in the Fe matrix increased with an increase of the annealing temperature. However, some holes appeared in the center of the sample annealed at a temperature of more than 830°C, which was detrimental to the subsequent rolling. The combination of the secondary cold rolling and annealing was beneficial to improve the composition homogeneity and magnetic properties of the sample. The magnetostriction coefficient (λ//) of the primary rolled sample was low, ∼4×10-6. After annealing and secondary cold rolling, the λ// of the sample increased to 9×10-6 and the λ// of the sample conducted by further annealing at 820°C for 20 h reached 27.5×10-6.
Effect of Co layer thickness on magnetic relaxation in Pt/Co/Ir/Co/Pt/GaAs spin valve J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 R.B. Morgunov, G.L. L'vova, A.D. Talantsev, O.V. Koplak, T. Fache, S. Mangin
Long magnetic relaxation (up to few hours) between stable magnetic states was analyzed in Pt/Co/Ir/Co/Pt/GaAs heterostructures of different Co layers thickness. The experimental data were compared to a large variety of theoretical models amongst which the Fatuzzo – Labrune one seems to be the more relevant. The contributions from domain nucleation and domain wall motion to magnetic relaxation of the spin valves were separated and evaluated. The increase of Co layer thickness suppresses the domain nucleation and enhances the domain wall propagation. The obtained data provide an understanding of the limitations of switching time in the spin valves of large area necessary for GMR biosensors.
Static magnetic susceptibility of radiopaque NiTiPt and NiTiEr J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-27 Drahomír Chovan, Abbasi Gandhi, Jim Butler, Syed A.M. Tofail
Magnetic properties of metallic alloys used in biomedical industry are important for the magnetic resonance imaging (MRI). If the alloys were to be used for long term implants or as guiding devices, safety of the patient as well as the medical staff has to be ensured. Strong response to the external magnetic field can cause mechanical damage to the patients body. In this paper we present magnetic susceptibility of nickel rich, ternary NiTiPt and NiTiEr to static magnetic field. We show that the magnetic susceptibility of these radiopaque alloys has values in low paramagnetic region comparable to the binary nickel-titanium. Furthermore, we studied the effect of the thermal and mechanical treatments on magnetic properties. Despite deviation from linear M(H)M(H) treated samples spanning small region around H=0H=0, the linearity of the M(H)M(H) and χ=dM/dHχ=dM/dH values suggest that these ternary alloys are safe to use under MRI conditions.
Glassy behavior of diluted Cu-Zn Ferrites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-26 Shahida Akhter, M.A. Hakim, S.M. Hoque, R. Mathieu, P. Nordblad
The magnetic behavior of Zn substituted Cu-Zn spinel ferrites having chemical formula Cu1-xZnxFe2O4 (x = 0.7, 0.8, 0.9 and 1.0) has been studied by SQUID magnetometry, by means of magnetic hysteresis, field-cooled (FC) and zero-field-cooled (ZFC) magnetization, memory effect and low field ac susceptibility measurements. These measurements suggest that the ferrimagnetic phase of the x ≤ 0.8 samples is gradually turned into a spin glass (x ≥ 0.9). The compound with x=0.9 exhibits the typical dynamical behavior of spin glasses, with indication of aging, rejuvenation and memory effects. The evolution of the magnetic properties of Cu-Zn spinel ferrites with substitution of Zn for Cu is discussed.
Magnetically-driven medical robots: an analytical magnetic model for endoscopic capsules design J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-26 Jing Li, Erfan Shojaei Barjuei, Gastone Ciuti, Yang Hao, Peisen Zhang, Arianna Menciassi, Qiang Huang, Paolo Dario
Magnetic-based approaches are highly promising to provide innovative solutions for the design of medical devices for diagnostic and therapeutic procedures, such as in the endoluminal districts. Due to the intrinsic magnetic properties (no current needed) and the high strength-to-size ratio compared with electromagnetic solutions, permanent magnets are usually embedded in medical devices. In this paper, a set of analytical formulas have been derived to model the magnetic forces and torques which are exerted by an arbitrary external magnetic field on a permanent magnetic source embedded in a medical robot. In particular, the authors modelled cylindrical permanent magnets as general solution often used and embedded in magnetically-driven medical devices. The analytical model can be applied to axially and diametrically magnetized, solid and annular cylindrical permanent magnets in the absence of the severe calculation complexity. Using a cylindrical permanent magnet as a selected solution, the model has been applied to a robotic endoscopic capsule as a pilot study in the design of magnetically-driven robots.
Stress induced by the striction of hybrid magnetoactive elastic composites J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-24 D.Yu. Borin, S. Odenbach, G.V. Stepanov
In this study we experimentally examine the mechanical stress induced by the striction of hybrid magnetoactive elastic composites in the direction parallel to an externally applied magnetic field. Elastic samples based on a polydimethylsiloxane matrix with embedded spherical magnetic soft carbonyl iron particles, spherical magnetic hard NdFeB-alloy particles as well as on a mixture of the two kinds of powder are under investigations. An effect of the structuring and pre-magnetization of the samples on the stress induced by the magnetodeformational effect is evaluated.
Predictions of thermomagnetic properties of Laves Phase compounds: TbAl2, GdAl2 and SmAl2 performed with ATOMIC MATTERS MFA Computation System J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-12-24 Rafał Michalski, Jakub Zygadło
Recent calculations of properties of TbAl2 GdAl2 and SmAl2 single crystals, performed with our new computation system called ATOMIC MATTERS MFA are presented. We applied localized electron approach to describe the thermal evolution of Fine Electronic Structure of Tb3+,Gd3+ and Sm3+ ions over a wide temperature range and estimate Magnetocaloric Effect (MCE). Thermomagnetic properties of TbAl2, GdAl2 and SmAl2 were calculated based on the fine electronic structure of the 4f8, 4f7 and 4f5 electronic configuration of the Tb3+ and Gd3+ and Sm3+ ions, respectively. Our calculations yielded: magnetic moment value and direction; single-crystalline magnetization curves in zero field and in external magnetic field applied in various directions m(T,Bext); the 4f-electronic components of specific heat c4f(T,Bext); and temperature dependence of the magnetic entropy and isothermal entropy change with external magnetic field - ΔS(T,Bext). The cubic universal CEF parameters values used for all CEF calculations was taken from literature and recalculated for universal cubic parameters set for the RAl2 series: A4=+7.164Ka04 and A6 =-1.038Ka06. Magnetic properties were found to be anisotropic due to cubic Laves phase C15 crystal structure symmetry. These studies reveal the importance of multipolar charge interactions when describing thermomagnetic properties of real 4f electronic systems and the effectiveness of an applied self-consistent molecular field in calculations for magnetic phase transition simulation.
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